1. Field of the Invention
This invention relates to a method for correcting angle induced error present in in vivo sound velocity estimations. More particularly, this invention relates to a method for estimating the angle of misdirection of a tracked ultrasound beam used in sound velocity measurements in conjunction with one or more tracking ultrasound beams.
2. Description of the Prior Art
Ultrasound techniques have been extensively used in the field of diagnostic medicine as a nontoxic means of analyzing the properties of in vivo (i.e., living) tissue. Ultrasound can be used for both tissue imaging as well as the measurement of the speed of sound in organic tissue. In particular, the speed of sound in an organ can be one indication of the presence of disease within that organ.
Tracked beam orientation is very important in obtaining accurate sound velocity measurements using beam tracking methods. A tracked beam may become misdirected for a variety of reasons, including improper transducer orientation, refraction, and improper phasing circuitry operation. Such misdirection produces an angle error in ultrasound velocity measurements.
In beam tracking methods used to determine in vivo sound velocity, such as those methods disclosed in U.S. Pat. No. 4,669,482 to Ophir, the misdirection of the tracked beam by an angle T introduces an error factor into the sound velocity estimate obtained by the method shown. This error factor is equal to [1-sin(T)]/cos(T) where T is the angle of misdirection of the tracked beam.